Electronic discharge tube and circuits therefor



July 27, 1948. J. KRUITHOF ETAL ELECTRONIC DISCHARGE TUBES AND CIRCUITSTHEREFOR Filed April 1, 1943 2 Sheets-Sheet 1 hllmlw JHCOB KP T OF L.CflBES July 27, 1948. J. KRUITHOF ETAL 2,445,782

ELECTRQNIC DISCHARGE TUBES AND CIRCUITS THEREFOR Filed April 1, 1943 2Sheets-Sheet 2 V Val- I- v v v \"i,

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gww/wbo'm JHCOB KPU/THOF' L. CHBES Patented July 27, 1948 "U l TED STATES ELECTRONIC'DISCHARGE TUBE AND CIRCUITS THEREFOR Jacob Kruithof andLucien Alfrcd Benoit Cabes, Antwerp, Belgium, assignors to InternationalStandard Electric Corporation,

New York,

N. Y., a corporation of Delaware Application April 1, 1943, Serial No.481,510 In the Netherlands February 24, 1941 'Section 1, Public Law 690,August 8,1946 Patent expires February 24, 1961 3 Claims.

. 1 This invention relates to a gaseous discharge tube having a closedenvelope in which electrodes are provided, which according to thepurpose and the use of the tube, may be arranged as cathode;

the invention also relates to control circuit arrangements in which suchdischarge tube is used.

'Itis already known to provide in a gaseous discharge tube a controllingelectrode between cathode and anode, whereby the starting of thedischarge between cathode and anode is determined by the value of thepotential applied to the controlling electrode. It is also already knownto provide additional grids in the tube, by

which a shifting of the point of starting of the paratus connected inseries with the discharge tube. The disadvantage of these known circuitsis that a certain quantity of energy is always taken from the controlcircuit, the control electrode being (during the discharge time) inconductive contact with the other electrodes by way of the ionized gasof the tube.

The purpose of the invention is to provide means to control directly thestarting and stopping of the main discharge and to use this control alsoto operate a consuming apparatus connected in series with the'dischargetube, withoutenergy being taken from the control circuit during thedischarge time.

According to the invention one or more con- "trol electrodes are mountedoutside the envelope of the tube, the control electrodes being made in'the'form of a metallic layer, band, ring, cover or any arbitrary form,each control electrode serving as a direct controlling electrode for thestarting and stopping of the main discharge to the anode.

As the control electrode or control electrodes is or are outside theenvelope of the tube, conductive contact with the other electrodesthrough the ionized gaseous inner space of the tube is avoided and nodecrease of energy of the control circuit takes place duringthedischarge condition of the tube.

#Accor'ding tonne of thercirouit arrangements of the invention, twoelectrodes, one of which or both may serve as cathodes, are mounted atequal distance from the anode, and an alternating potential ofsufficient magnitude is applied between the two first-named electrodesto cause a glOW discharge between them.

This glow discharge may be considered as a fictive filament, whichcauses an emission of electrons. The maximum value of the alternatingpotential and the magnitude of the positive potential applied to theanode, are, when added algebraically, not sufficient to initiate anindependent discharge between the fictive filament and the anode;however, this discharge does take place as soonas a potential is appliedto the control electrode (or to one of the control electrodes) of such avalue that will sufiiciently a'cthe two cathodes and the anode, and thedischarge will be extinguished when the algebraical 'sumof thesepotentials becomes less than required for the maintenance of thedischarge.

Between the D. C. source and the anode, or at another point in serieswith the discharge space between anode and cathode, a consumingapparatus, e. g. a relay, may be provided which responds to the changesof the potential applied to a control electrode.

The advantage thereof is that the energy, required for the operation ofthe consuming apparatus, is only taken from the sources of potentialconnected in series to the tube, and no energy is taken from the controlelectrode.

A second circuit according to the invention is arranged in such a waythat a rectified A. C. potential is connected to the anode, and theoathode (or more than one cathode connected in parallel) is connected tothe negative terminal of a D. C. source through a consuming apparatus,which is either shunted or not by a capacity, and the sum of this D. C.potential and the maximum value of the rectified A. C. potential at theanode is less than the potential required to change the invisibledischarge to the anode into an independent visual discharge; the

starting of the visual discharge is controlled by a potential ofsufiicient value applied to the control electrode or to one of thecontrol electrodes, while the extinguishing of the discharge takes placeafter the decrease of the potential applied to the control electrode, assoon as the sum of the rectified A. C. potential and the D. C. potentialbecomes less than that required for maintaining the discharge.

Two embodiments of the invention are shown in the accompanying drawings.

Figure 1 shows a circuit arrangement in which an A. C. potential isapplied between two electrodes within the tube and in this way a fictivefilament is formed by the glow discharge between these electrodes. Theconsuming apparatus to be controlled is connected in the anode circuitof the tube.

In Figure 2 two electrodes serving as cathodes are connected inparallel, and the consuming apparatus to be controlled is connected inthe cathode circuit of the tube. Curves illustrating the operation ofthe circuit arrangement of Figure 1 are shown in Figures 3a and 31),while Figures 4a and 4b are curves which relate to the circuitarrangement of Figure 2.

In Figure 1 three electrodes C, C" and A are arranged within an envelopefilled with gas at low pressure.

An A. C. source is connected to a transformer T from which a potentialVl is applied between the ends of the secondary winding to theelectrodes C and C", over which a glow discharge is established,bringing about an emission of electrons.

This glow discharge forms a fictive filament or a source of electrons.

' Practically equidistant from electrodes C and C the anode A isarranged, a positive potential V being applied to the anode from sourceB. The potentials VI and V are connected therefore in this circuitarrangement in series with electrodes C and A of the tube. A loaddevice, such as relay R, is also connected in the anode circuit.

In Figure 1 four potentials are of practical interest:

(1) A lighting potential Va, required to cause the starting of a glowdischarge between the electrodes C and C;

(2) A potential Vb, which is just suificient to maintain such a glowdischarge between the electrodes C and C";

(3) A lighting potential Vc, required to cause the starting of a glowdischarge between C or C" and A;

(4) A potential Vd, which is just suflicient to maintain this last nameddischarge.

The values of V and VI are selected such that the maximum potential ofVI is equal to or larger than Va; further than the V+VI max. is lowerthan V0, and V is lower than Vd.

From the last named condition it follows that the field ACC" is of toosmall value to cause the Townsend discharge to change into anindependent visual discharge; in other words, the electrons emitted bythe fictive filament C'C" will not be sufficiently accelerated on theirway to the anode to energize the anode circuit through the maindischarge space of the tube.

Outside the tube a control electrode H is arranged and may have anarbitrary form, for example, it may be formed as a cap, a ring or aband. An appropriate form, however, consists in a metallized layer onthe glass of the tube.

Normally such a potential is applied to the electrode H that theelectro-static field between H and C, C" is opposite to the field C'C"A,so that the electrons from the fictive filament encounter still moreresistance in order to reach the anode.

The situation is completely changed as soon as apositive potential isapplied to the electrode H, as now the two fields are supporting eachother, and therefore the ionization is (at a predetermined value of thepositive potential of H) increased to such an extent that the invisibledischarge of Townsend changes into a visual discharge, the dischargetakes place in the tube and a current flows through the anode circuit,in which the consuming apparatus R is inserted. As soon as the potentialof H is made negative again, the accelerated movement of electrons tothe anode is decreased and a moment comes at which the tube willextinguish, i. e. when the potential VI passes the point at which thispotential, together with the D. 0. potential V, becomes less than thevalue Vd. The above is illustrated by Figure 3a.

This figure shows that the A. C. potential VI superposed on the D. C.potential will, in the normal condition of the tube, (that is to saywhen no positive potential is connected to a control electrode) neverreach the value Vc, i. e. the potential which in the normal condition ofthe tube causes the main discharge. By connecting the control potentialto H an amplification of the electrostatic field is obtained, which hasthe same effect as if the value Vc were decreased to Vcl, as shown inFigure 3b. This discharge is established as soon as the potential curvereaches the value Vcl, and is extinguished when the potential curvedecreases to the value Vd. During the following cycle of the A. C.potential, if the potential of the controlelectrode H is still present,the discharge takes place again as described above. The discharge isdefinitely extinguished when, after decrease of the potential of H, thedecreasing potential curve intersects again the line Vd; or when, at atime when the control potential is taken away from H, no discharge takesplace. Current flows in the anode circuit during the periods shown byshaded areas of Figure 3b.

The consuming apparatus R receives rectified current pulses as long as apotential of sufilcient value is present on the control electrode, andthe consuming apparatus may be supplied with constant current in one ofthe different known ways during the entire duration of connecting thepotential to H, for example, by connecting a capacity in parallel to R.

From the above it appears that control electrode H provides very simplemeans to control the action of the tube so that the consuming apparatusresponds in accordance with the polarity and value of the potentialapplied to the control electrode. I V

Figure 2 shows a second embodiment of the invention. Here the electrodesC and C are connected in parallel, so that there is no question any moreof a fictive filament. They are biased by source B to a negativepotential V with respect to ground G, which potential is lower than Vd,i. e.,the potential whichis just sufficient to maintain the dischargebetween C, C" and A.

A pulsating DC. potential V2 originating from a rectified A. C.potential is applied to the anode. As shown in Figure 2, the rectifiedpotential is supplied by a rectifier consisting of a transformer Tatheprimary of which is conhected to a suitable source of alternatingcurrent. The mid-point of the secondary is grounded, and the ends of thesecondary winding areconnected through rectifier elements Ru and Rb toone terminal of a load resistance Re, the other terminal of thisresistance being connected to the grounded mid-point connection. Theanode A is connected to the common connection between rectifier elementsRa and Rb and resistance Re. The arrangement produces full-waverectification, and the rectified potential V2 developed acrossresistance Re is applied to the anode A.

This rectified potential is selected in such a way that V+V2 max. islower than the lighting potential Vc for a discharge between '0" and Aand the sum is greater than Vd.

If a negative potential is applied to the control electrode H, then 'aninsufficient number of electrons are freed to convert the Townsenddischarge into an independent ionized discharge.

If, however, a positive potential of sumcient magnitude is connected tothe control electrode, then the independent discharge will take place,since both fields aid each other in giving sufficient acceleration tothe electrons.

The discharge extinguishes as soon as the potential of the rectifiedalternating current, together with the direct current V, becomes smallerthan the value Vd.

The above is illustrated in Figures 4a and 412. Figure 40. representsthe condition when no positive potential is present on H. The rectifiedA. C. potential V2 is superposed on the D. C. potential V in the maindischarge space, but the maximal sum of the values of these potentialsdoes not normally reach the starting potential V0. The connecting of apositive potential of sufiicient value to H has the same result as ifthe value Vc were reduced to Vcl, as shown in Figure 4b. The dischargenow takes place at the moment the potential curve reaches at least thevalue Vcl and continues until, by the decrease of the potential, theline Vd is reached. Then at a following increase of potential, thepotential on H being still present, the discharge takes place again asdescribed above. The discharge is definitely extinguished when, afterthe decrease of the potential of H, the potential curve reaches the lineVd; when the rectified A. C. potential V2 decreases, or when thepotential is removed from H, no discharge occurs. Rectified currentpulses pass through the main discharge space of the tube and through theconsuming apparatus R, which is now connected in series between theelectrodes C, C and the negative terminal of the direct current sourceB.

The condenser 0 parallel to the consuming appar'atus '(relay R) servesto smooth the rectified alternating current flowing through R; moreover,this condenser promotes the extinguishing of the main discharge.

In order to shorten the periods of no current for the consumingapparatus as much as possibio, and also with the aim to make the timeduring which the consuming apparatus responds equal, as accurately aspossible, to the time during which potential is connected to H, it isadvisable to select the frequency of the potentials VI and V2 as high aspossible. This frequency is, however, limited to an upper limit by thedeionization time of the tube.

When during the discharge condition the potential decreases to the valueVd, the discharge will stop immediately, but the gas in the tube stillremains in an ionized condition for a short time.

During this time the potential curve may again reach the value Vd, andthe discharge condition would again occur, even if the potential on H beremoved.

In order to prevent this, it is necessary to select the frequency of VIor V2 such that de-ionization can take place between two consecutivedischarge periods.

The time of de-ionization of the tube causes a certain delay in theoperation of the consuming apparatus in response to the potentialsapplied to H.

Instead of connecting a rectified A. C. potential to the anode as inFigure 2, an A. C. potential may be used if desired. In this case theoperation will be as shown in Figures 3a and 319. Here the relative timeavailable for de-ionization is greater than with a rectified A. C.potential, so that the frequency may be increased.

Instead of only one control electrode H, a larger number of controlelectrodes may be provided, by which operation with more controlpotentials is possible. Moreover the shape and arrangement of thecontrol electrodes may differ from each other.

It is clear that in the arrangements described, operation of theconsuming apparatus requires energy to be taken only from the potentialsources V and VI, and no energy is taken from the control electrode.

We claim:

1. Control apparatus comprising a discharge tube containing an anode, acathode and a third electrode, an external control electrode on theenvelope of the tube, said cathode and said third electrode being spacedsubstantially equal distances from said anode, and including means forapplying a direct current potential between said anode and said cathodeand means for applying an alternating potential between said cathode andsaid third electrode to establish an ionized discharge between saidelectrodes, said discharge forming an electron emitting fictivefilament, the algebraic sum of said alternating potential and of thepotential applied to said anode being insufiicient normally to initiatean independent discharge between said fictive filament and the anode,but being efiective to establish said independent discharge when apositive potential is applied to said control electrode.

2. Control apparatus comprising, in combination, a gaseous dischargetube having a closed envelope with an external control electrode andcontaining three spaced electrodes comprising a cathode, an anode and athird electrode, said cathode and said third electrode being spacedsubstantially equal distances from said anode, a source of alternatingcurrent potential connected between said cathode and said thirdelectrode to establish an ionized discharge between said electrodes,said discharge forming an electron emitting fictive filament, a workcircuit including a source of direct current connected between saidanode and one of the electrodes of said fictive filament, said directcurrent potential being insufiicient normally to establish anindependent discharge between said fictive filament and the anode, andcontrol means for successively accelerating the electrons supplied fromsaid fictive filament to said anode to a value sufiicient to establishan independent discharge between said anode and said fictive filament.

3. Control apparatus comprising, in combination, a gaseous dischargetube having a closed envelope containing an anode and two spaced cathodeelectrodes, means for applying an alternating potential between said twocathode electrodes for establishing a glow discharge between the cathodeelectrodes, a control electrode arranged outside of said envelope, aWork circuit including a source of direct current potential connectedbetween said anode and said cathode electrodes, the algebraic sum ofsaid direct and alternating potentials being insufficient normally toestablish an ionized discharge between said anode and cathodeelectrodes, and a control circuit for selectively applying a sufiicientpositive potential to said control electrode to establish an ionizeddischarge between said anode and cathode electrodes, said work circuitincluding a consuming device.

JACOB KRUITHOF. LUCIEN ALFRED BENOIT CABES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITEDSTATES PATENTS Number Name Date Re. 20,345 Schaberle Apr, 27, 19371,410,702 Meyer Mar. 28, 1922 1,661,579 Rollinson Mar. 6, 1928 1,863,702Smith June 21, 1932 1,938,742 Demarest Dec. 12, 1933 1,984,877 Jobst etal Dec. 18, 1934 2,001,836 Craig May 21, 1935 2,103,439 Swart Dec. 28,1937

